The present invention relates to a photopolymerizable mixture which contains a polymeric binder, a polymerizable compound having at least two acrylate or alkacrylate groups in the molecule, and a photoinitiator combination.
Photopolymerizable mixtures which contain acrylates and/or methacrylates as photopolymerizable compounds are known. For the production of photoresist materials, in particular dry photoresist coatings, mixtures are preferred which contain acrylates or methacrylates having urethane groups in the molecule and which can be developed using aqueous alkaline solutions. Such mixtures are described, for example, in German Offenlegungsschrift No. 2,822,190, German Auslegeschrift No. 2,115,373, German Patent No. 2,361,041 and U.S. Pat. Nos. 3,850,770 and No. 3,960,572.
On the other hand, photopolymerizable mixtures are also known which, in order to increase the photosensitivity, contain certain combinations of photoinitiators and activators, for example carbonyl-group-containing initiators and tertiary amines. Such mixtures with a synergistic action are described, for example, in German Offenlegungsschriften No. 2,602,419 and No. 2,251,048 and U.S. Pat. No. 3,759,807. A disadvantage of these mixtures which contain low-molecular-weight amines is that they have a short shelf life since the amines can easily bleed out, in particular from thin coatings.
In Japanese Patent Application No. 50/129,214, a photopolymerizable mixture is described which contains a tetra(meth)acrylate of a N'N'N',N'-tetrahydroxyalkylalkylenediamine as polymerizable compound. The tetrafunctional compound serves as a crosslinking agent.
It is furthermore known that the free-radical polymerization of ethylenically unsaturated compounds can be initiated by irradiation with visible light in the presence of photoreducible dyes and reducing agents, for example amines (U.S. Pat. No. 3,097,096). However, these initiator combinations are essentially employed only in aqueous solution or in combination with water-soluble binders.
Initiator combinations of photoreducible dyes and other reducing agents are described in U.S. Pat. No. 3,597,343 and No. 3,488,269. Photopolymerizable mixtures which contain exclusively photoreducible dyes as initiators have hitherto not been employed in practice due to their inadequate photosensitivity.
In Japanese Patent Application No. 54/151,024, a photopolymerizable mixture is described which contains an initiator combination of a merocyanine dye and a trihalomethyl-substituted s-triazine and is sensitive towards visible light, for example an argon laser. However, the sensitivity of these mixtures towards visible laser light is inadequate for economic utilization.